I did a fair amount of research on protein skimmers prior to purchasing. I chose the Tunze 9002 as I was looking for a unit that performed well, didn't dwarf my 37-gallon tank, and was minimal in appearance (trying to keep a clean look).
While I only have 3 fish so not over-stocked by any means, I am certainly surprised at the skimmate this unit pulls out of the water column ... especially considering how simple and basic the unit is. It's also so quit that I have to touch it to feel if the unit is actually working.
Pricey compared to what you mention above but worth considering ...
Tunze Nano DOC Protein Skimmer 9002